Four normal adults were maintained for 44 days on a controlled diet which was estimated to furnish 600 μg of thiamine per 1000 cal. Basal 24-hour urinary excretions of thiamine were higher at the first of the period than at the end. Supplements of thiamine given during the pre-experimental period undoubtedly caused elevations in values for the first 2 weeks of the study. Four urinary excretion tests for thiamine were studied. Values for 24-hour excretions of thiamine for the last 4 weeks ranged from 100 to 224 μg per day. Average percentages of thiamine intake excreted ranged from 9 to 13%. Responses to a 5-mg. oral test dose at the end of the study ranged from 15 to 22% recovery in 24 hours. Responses to 1-mg intramuscular test doses toward the beginning of the study ranged from 15 to 24% recovery. At the end of the study they ranged from 8 to 21% recovery, or 193 to 403 μg excretion in 24 hours. When the urinary excretion values recorded for “normal” subjects were used as standards for comparison, the nutritional status of these subjects with respect to thiamine was not judged to be the same by all four criteria. More data are needed to establish the range of normal values for these urinary excretion tests, and their relative sensitivity.